Transcorporeal spinal decompression and repair system

ABSTRACT

A system and method are provided for making an access channel through a vertebral body to access a site of neural compression, decompressing it, and repairing the channel to restore vertebral integrity. System elements include an implantable vertebral plate, a guidance device for orienting bone cutting tools and controlling the path of a cutting tool, a bone cutting tool to make a channel in the vertebral body, a tool for opening or partially-resecting the posterior longitudinal ligament of the spine, a tool for retrieving a herniated disc, an implantable device with osteogenic material to fill the access channel, and a retention device that lockably-engages the bone plate to retain it in position after insertion. System elements may be included in a surgery to decompress an individual nerve root, the spinal cord, or the cauda equina when compressed, for example, by any of a herniated disc, an osteophyte, a thickened ligament arising from degenerative changes within the spine, a hematoma, or a tumor.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 12/210,089filed Sep. 12, 2008 which claims priority to U.S. Provisional PatentApplication No. 60/972,192 of Lowry et al., entitled “Transcorporealspinal decompression and repair system and related method”, as filed onSep. 13, 2007.

FIELD

The invention relates to devices and methods of spinal surgery. Moreparticularly, the invention provides an implant for use in spinal repairsurgery and a method for preparing the vertebral volume to receive theimplant.

INCORPORATION BY REFERENCE

All publications, patents and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication, patent or patent application wasspecifically and individually indicated to be incorporated by reference.

In particular, U.S. patent application Ser. No. 11/855,124 of Lowry etal. (filed on Sep. 13, 2007, entitled “ Implantable bone plate systemand related method for spinal repair”), U.S. Provisional PatentApplication 60/972,199 of Lowry et al. (filed on Sep. 13, 2007, entitled“Device and method for tissue retraction in spinal surgery”) as well asthe U.S. patent application Ser. No. 12/210,109, U.S. Provisional PatentApplication No. 60/976,331 of Lowry et al. (filed on Sep. 28, 2007,entitled “Vertebrally mounted tissue retractor and method for use inspinal surgery”), and U.S. Provisional Patent Application No. 60/990,587of Lowry et al. (filed on Nov. 27, 2007, entitled “Methods and systemsfor repairing an intervertebral disk using a transcorporal approach”)are all incorporated by this reference.

BACKGROUND

The performance of cervical discectomy, excision of tissue, and neuralelement decompression procedures have become standard neurosurgicalapproaches for the treatment of disorders of the spine and nervoussystem, as may be caused, for example, by disc degeneration,osteophytes, or tumors. The compressive pathologies impinge onto aneural element, causing a compression of nerve tissue that results in asymptomatic response such as loss of sensation or strength, occurrenceof pain, or other related disorders. The majority of these proceduresare performed with an anterior approach to the cervical spine. Disc andbone tissue are removed, a neural decompression is achieved, and aspinal repair procedure is performed.

The current conventional repair procedure includes a vertebral fusion inwhich a biocompatible implant is inserted and secured between theaffected adjacent vertebrae. A bone plate is then is rigidly attached tothe two vertebrae adjacent to the implant, immobilizing these vertebralsegments and preventing the expulsion of the implant from theintervertebral space. Subsequently, osteogenesis of the vertebrae intothe implant occurs, and ultimately the adjacent vertebrae fuse into asingle bone mass. The fusion of the vertebral segments, however, canlead to problematic results. For example, the immobility of the fusedvertebral joint is commonly associated with the progressive degenerationof the adjacent segments, which, in turn, can lead to degeneration ofthe intervertebral discs on either side of the fused joint.

Implantation of an artificial disc device offers an alternate approachto vertebral fusion. The objective of the artificial disc device is topreserve the relative motion of the vertebrae across the joint and torestore normal articulating function to the spinal column. In spite ofthe benefits that these procedures have brought to patients, both fusionand disc replacement have inherent problems. The surgeries areextensive, recovery time is relatively long, and there is often a lossof function, particularly with the use of fusion implants. The long-termbiocompatibility, mechanical stability, and durability of replacementdisc devices have not been well established. Further, there is noclinical consensus that the use of a replacement disc reduces the riskof adjacent segment degeneration.

Methods for surgery on the spine and cervical discs from an anteriorapproach were first developed in the 1950's, and a number of variationshave been developed since then. Each anterior cervical discectomyprocedure, however, has had to face the challenge represented byremoving the tissue overlaying the compressing lesion (i.e., theherniated disc material, osteophyte or tumor) after having dissectedthrough the soft tissue anterior to the spine. Early procedures exposedthe compressing tissue by first making a cylindrical bone-and-discdefect in the spine centered on the disc space in sagittal and coronalplanes, and generally following the plane of the disc itself. Laterprocedures made use of a rectangular, box-like defect in the disc spacecentered on the disc space and generally following the plane of thedisc.

Procedures recently developed by Jho (referenced below) were motivatedby the concern that procedures like those described above destroyed moreof the natural disc tissue than was necessary to remove alaterally-positioned disc herniation or osteophyte (a bone spur). Analternative procedure, an uncovertebrectomy, was therefore developedthat involved the removal of only the lateral-most aspect of the discspace, and the vertebral bone above and below it, which togethercomprise the entire uncovertebral joint. (See Choi et al., “Modifiedtranscorporeal anterior cervical microforaminotomy for cervicalradiculopathy: a technical note and early results”, Eur. Spine J. 2007Jan. 3; Hong et al., “Comparison between transuncal approach and uppervertebral transcorporeal approach for unilateral cervicalradiculopathy—a preliminary report”, Minim Invasive Spine Surgery, 2006October; 49 (5):296-301; and Jho et al., “Anterior microforaminotomy fortreatment of cervical radiculopathy: part 1: disc-preserving functionalcervical disc surgery”, Neurosurgery 2002 November; 51 (5 Suppl.):S46-53.) This new type of procedure allows much of the disc space toremain untouched. While preserving more of the disc space and discmaterial than its predecessor procedures, the uncovertebrectomynevertheless does obliterate the uncovertebral joint, and there isconcern in the field regarding the eventual development of spinalinstability at that disc level. Further, drilling bone at high speedadjacent to the nearby vertebral artery and sympathetic nerve processincreases the concern of a higher risk of vertebral artery, secondarysoft tissue injury, and Homer's Syndrome.

In another refinement of the uncovertebrectomy procedure, an anteriorcervical microforamenotomy, the uncinate process and the lateral disctissue may be left largely intact as a hole is drilled through the boneadjacent to the disc space near the uncinate process. In bothuncovertebrectomy and anterior microforamenotomy, the exposure anddecompression of the neural elements generally follow the plane of thedisc space. While vertebral artery injury and spinal instability remainconcerns with both procedures, the risk associated with anteriormicroforamenotomy is considered less than that of uncovertebrectomy.

An additional refinement of both uncovertebrectomy and anteriormicroforamenotomy is a transcorporeal decompression procedure (alsoreferred to as an upper vertebral transcorporeal foramenotomy or atranscorporeal discectomy) may have advantages. This procedure differsfrom its disc space-preserving precedent procedures in several ways.First, the axis of the access hole drilled to expose the compressingpathology (e.g., herniated disc fragment) does not parallel the plane ofthe disc, but instead entirely avoids the disc space plane anteriorlyand captures the disc only at its most posterior aspect. Second, whileuncovertebrectomy and anterior cervical microforamenotomy are applicableonly to lateral pathology, the transcorporeal decompression ispotentially applicable to compressing pathology located laterally in thedisc space region, bilaterally, or in the midline. Further, theprocedure is performed from a substantially medial position on thevertebra assuring maximal distance from the vertebral artery and othersensitive soft tissue and thereby minimizing the risk of accidentalinjury.

Multiple technical challenges remain, however, in optimizing thetranscorporeal cervical decompression procedure for general surgicaluse. First, manually orienting and controlling a hand-held cutting toolto make an access channel is a subjective and error-prone procedure. Thetarget pathology is wholly behind and/or within the bony structure ofthe vertebra and is not visible in any way when approached from atraditional anterior approach to the cervical spine. As the channel isessentially being driven blindly, it can easily fail to capture thetargeted pathology being within the range of the posterior opening ofthe access channel. Consequently the surgeon needs to prolong theprocedure, and explore the space by excising tissue until the pathologyis found. The exploration typically leads to the access channel becominglarger than necessary and undesirably irregular, thus puttingsurrounding bone at risk of fracturing during or after the procedure.Given the proximity of many target pathologies to the uncovertebraljoint and the vertebral artery, it is likely that exploration of thespace will lead to removal of the stabilizing bone and disc tissue. Thistissue damage or loss can cause spinal instability, and may furtherresult in accidental perforation of the vertebral artery.

Second, a manual drilling process increases the risk of over penetrationinto the spinal canal, with highly undesirable consequences.

Third, the posterior longitudinal ligament, once exposed in the accesschannel, can be difficult to open. The objective is to remove theligament cleanly from the access channel area so as to provideunobstructed visualization of the compressed neural tissue. Currentsurgical techniques are subjective and time-consuming, often producing ashredding of the ligament within the access channel rather than itsremoval therefrom, thereby impeding the visualization of the underlyingtarget pathology or dura mater protective layer.

Fourth, currently available micro surgical instruments are notwell-suited for retrieving the herniated disc or bone fragments that maybe found deep to the posterior longitudinal ligament.

Fifth, after the decompression is complete, the present solutions forfilling the void remaining in the vertebra are not completelysatisfactory. Demineralized bone matrix putties or similar materials canfill the defect but they offer no resistance to the normal compressingor torsional forces until calcification occurs. Such materials may alsoimpose a new source of compression on the exposed neural structures iftoo much putty is applied or if the vertebra deforms or sustains acompression fracture subsequently because of the absence of an implantthat sufficiently resists compressive forces.

Sixth, after a solid implant plug is placed in the surgically-formedaccess channel, there is presently no anterior cervical plate suited topreventing its outward migration. Currently available anterior cervicalplates are designed to be placed across two or more adjacent vertebraeat or near the midline, not laterally, as would be needed for lateralcompressing lesions. Existing plates also are designed asmotion-restriction or motion-prevention devices to be placed bridgingacross a disc space rather than onto a single vertebral body,consequently they are too large and are counterproductive in theapplication such as that described above where the objective is topreserve the articulation and relative motion of the adjacent vertebrae.

Accordingly, there is a need for a system and method whereby anycompressing spinal pathology may be removed or moved so as to decompressthe neural elements involved while desirably also (1) preserving nativedisc and bone tissue and the natural motion of the spine with naturaldisc material, (2) minimizing the risk of injury to the vertebralartery, (3) minimizing the risk of structural spinal instability, (4)minimizing the risk of an inadequate decompression, (5) minimizing therisk of injury to the protective dura mater layer, (6) minimizing therisk of post operative bleeding and/or (7) minimizing the risk of asubsequent vertebral body fracture due to an unrepaired defect withinit.

SUMMARY OF THE DISCLOSURE

The invention provides a system and method for forming and repairing anaccess channel through a vertebral body, typically a cervical vertebralbody, for the purpose of gaining access to a site in need of a medicalintervention. In its formation, the channel originates on the anteriorsurface of the vertebral body, and it then provides access from theanterior approach. The channel follows a prescribed trajectory to aprescribed exit on the posterior surface of the vertebral body, andprovides an opening at the site of sufficient size to address themedical need. The access channel is typically formed in cervicalvertebral bodies. The nature of the medical need typically includes theneed for a decompression procedure, as may occur as a result of aproblematic portion or the whole of a herniated disc, an osteophyte, athickened ligament, a tumor, a hematoma, a degenerative cyst, or anyother compressing pathology. The medical intervention may be as minimalas observing the site, or performing exploration, or it may include adiagnostic procedure, or delivering a therapy, or it may include asurgery. A typical surgery performed through the access channel caninclude decompressing a neural element, such an individual nerve root, aspinal cord, or a cauda equina.

The system of the invention further includes an implantable bone repairdevice having an external geometry complementary to the internalgeometry of the access channel, and a method for repairing or healingthe channel by implanting such device. Some embodiments of the deviceinclude materials that are biocompatible, biologically absorbable, orany material known to be able to substitute for bone, and to be able tobe stably and effectively integrated into bone. The device may furtherinclude as well as biologically active agents, such as osteogenicagents, that promote healing of the wound represented by the accesschannel, and fusion of the device such that it integrates into thevertebral body.

In some embodiments, the implantable bone repair device includes anassembly with a porous body that includes actual bone tissue. Such bonetissue may be provided by the bone removed during the formation of thechannel itself, or it may come from another site from the patient as anautologous graft, or it may be provided by a separate donor.

The system to form and repair an access channel includes a bone cuttingtool with a cutting element, a bone plate configured to be secured tothe anterior surface of the vertebral body and having an opening sizedto receive the cutting element; and a trajectory control sleeveconfigured to detachably engage the bone plate and having a cylinderconfigured to receive the cutting element. The bone plate and thetrajectory control sleeve, when mutually engaged, are configured tocooperate to guide the cutting element to form the access channel with aprescribed trajectory from the anterior entry to the prescribedposterior opening.

Embodiments of a method for prescribing of the point of anterior entryand the channel trajectory toward the posterior opening are typicallyprovided by a physician who observes the cervical spine of the patientradiographically. From such observation of patient anatomy and the siteof pathological interest, the physician prescribes a trajectoryaccording to a cranio-caudal axis and a medial lateral axis with respectto a point of entry on the anterior surface of vertebral body. Suchradiographic observation may occur before the attachment of the boneplate, to be summarized below, and/or after the attachment of the boneplate.

Returning to summarizing the system for forming the access channel, someembodiments include fixation elements to secure the bone to the anteriorsurface of the vertebral body. The bone plate may include openings toaccommodate fixation elements to secure the bone plate to the anteriorsurface of the vertebral body. In some embodiments, the bone plate andfixation elements are configured of a biocompatible material. In someembodiments, the bone plate and the fixation elements have a compositionand structure of sufficient strength that that the bone plate may bepermanently implanted.

Embodiments of the trajectory control sleeve may be configured to directthe bone cutting tool on a trajectory prescribed by the method above,the prescribed trajectory being an angle according to a cranio-caudalaxis and a medial lateral axis with respect to a reference planetangential to the access channel entry on the anterior surface ofvertebral body.

Embodiments of the bone plate provide a reference plane such that thetrajectory control sleeve, when secured to the bone plate, may beconfigured with a range of angles formed on two axes with respect to theplane of the bone plate, a cranio-caudal axis and a medial lateral axis,the range of the angles varying between about 1 degree and about 30degrees from an angle perpendicular to the plate. In typicalembodiments, the range of the angles varies between about 10 degrees andabout 30 degrees from the perpendicular angle. In some embodiments, thesystem includes a plurality of trajectory control sleeves, the sleevesvarying in regard to angles formed with respect to a plane representedby the bone plate when secured thereto, the angles ranging between about10 degrees and about 30 degrees cranio-caudally from a perpendicularangle.

In some embodiments, the trajectory control sleeve and the bone platehave mutually-engageable features that orient the engagement of thetrajectory control sleeve on the bone plate in a configuration thatallows the trajectory control sleeve to guide the cutting tool into thevertebral body with the prescribed trajectory. And in some embodiments,the trajectory control sleeve includes a contact surface for engaging acorresponding surface on the bone cutting tool, the surfaces configuredso as to limit the penetration of the cutting tool into the vertebralbody to a prescribed depth.

In some embodiments, the posterior surface of the bone plate includesone or more penetrating elements configured to impinge into thevertebral bone tissue to improve fixation and resist the torsionalforces associated with bone cutting procedures. In some embodiments, thebone plate includes an anatomically-orienting feature to establish theposition of the bone plate relative to the medial centerline of thevertebral body. In some embodiments, the bone plate includes abiocompatible material. And in some embodiments, at least a posteriorsurface of the bone plate is of sufficiently porous composition tosupport in-growth of bone.

In various embodiments, the bone-cutting tool is any of a drill, areamer, a burr, or cylindrical cutting tool, such as a core cutter or atrephine. In some of these embodiments, the cutting element of thebone-cutting tool has a cutting diameter of between about 5 mm and about7 mm.

As noted above, embodiments of the implantable bone repair device havean external geometry complementary to the internal geometry of theaccess channel. These bone repair device embodiments may be sized to beinsertable through an opening of the bone plate, the opening also beingsized to receive the bone cutting element. In some embodiments, the bonerepair device includes an abutting surface configured to engage acorresponding surface of the bone plate through which it is implanted,the engagement of these surfaces adapted to prevent the bone repairdevice from penetrating too deeply into or through the access channel ofthe vertebral body. In some embodiments, the bone repair device includesreceiving features in or on its anterior surface configured toaccommodate the attachment of an insertion tool.

In some of these embodiments, bone repair device and the bone plate havemutually engageable orientation and locking features. In variousembodiments, the locking engagement results from the application of anaxial force to snap the locking feature into a corresponding retainingfeature of the bone plate. In other embodiments, the locking engagementresults from the application of a torsional force to engage the lockingfeature into a corresponding retaining feature in or on the bone plate.

In some embodiments of the surgical system the bone repair devicecomprises a porous cage with a porosity sufficient to permit throughmovement of biological fluids, such as blood, and bone cells. Thecomposition of the porous cage portion of the device may include any ofa polymer, a metal, a metallic alloy, or a ceramic. An exemplary polymermay polyetheretherketone (PEEK), which may be present in the form ofPEEK-reinforced carbon fiber, or hydroxyapatite-reinforced PEEK. In someembodiments of the bone repair device with a porous cage, the porouscage device includes a closeable opening through which harvested bonematerial (such a native bone from the access channel site) may bepassed. And in some of these embodiments, the porous cage deviceincludes a closeable cap configured to increase pressure on theharvested bone within the cage as the cap is closed. Further, someembodiments include an internal element adapted to enhance compressiveforce applied to the contents of the porous cage upon application ofcompressive force to the cage, such force inducing extrusion ofharvested bone and blood from within the cage through its porousstructure to the external surfaces of the cage.

Some embodiments of the surgical system include a trajectory and depthvisualization device. In some of these embodiments, the trajectory anddepth visualization device includes a radio-reflective feature so as toconfirm the location of the bone plate device on the appropriatevertebral body and to facilitate the extrapolation of the projectedtrajectory of the bone cutting tool using a radiographic image. In someembodiments, the trajectory and depth visualization device includesvisual markings to indicate the distance from the point of contact withthe vertebral body and cutter penetration control feature on the bonecutter guide device.

A method for performing a procedure through a vertebral body overlayinga site in need of a medical procedure includes attaching the bone plateon the anterior surface of the vertebral body, engaging the trajectorycontrol sleeve to the bone plate, inserting a bone cutting tool throughthe trajectory control sleeve, and forming an access channel body byremoving bone with the bone cutting tool (the channel having acenterline co-incident with the centerline of the trajectory controlsleeve through the vertebral), disengaging the trajectory control sleevefrom the bone plate, and performing the medical procedure through theopen space provided by the access channel and the opening on theposterior surface of the vertebral body.

The access channel follows a prescribed trajectory from an anteriorentry point to a prescribed opening on a posterior surface of thevertebral body in the locale of the site in need of the medicalprocedure. The prescription for the points of entry and exit and thevectors of the access channel are determined by radiographicobservations and measurements, as summarized above. In some embodimentsof the method, forming the access channel includes forming the channelwith a constant, circular cross-section along a single, straight axisaligned with the trajectory control sleeve.

Before engaging the trajectory control sleeve to the bone plate, themethod may include selecting the sleeve to be used in the procedure suchthat when the sleeve and the bone plate are engaged, the sleeve has anangular orientation relative to the bone plate that is consistent withthe prescribed trajectory of the access channel. Further, beforeattaching the bone plate to an anterior vertebral surface, the methodmay include exposing one or more vertebral bodies in a spinal column byanterior incision. Further still, after performing the medicalprocedure, the method may include leaving the bone plate attached to thevertebral body.

In some embodiments of the method, after engaging the trajectory controlsleeve to the bone plate, the method may include inserting a radiopaquelocating device into the trajectory control sleeve device,radiographically observing the locating device and determining therefroman extrapolated trajectory of the access channel toward the posteriorsurface of the vertebral body, and verifying that the extrapolatedtrajectory is consistent with the prescribed trajectory such that thepoint of exit at the posterior surface is proximal to the targeted siteof interest.

In some embodiments of the method, after engaging the trajectory controlsleeve to the bone plate, the method may include inserting adepth-measuring device into the trajectory control sleeve device toestablish an optimal depth of penetration of the bone-cutting tool intothe vertebral body, the depth being influenced by the disposition of thebone plate against a variable topography of the anterior surface of thevertebral body.

In some embodiments, after the completing the medical procedure throughthe access channel, the method further includes repairing the accesschannel with an implantable bone repair device, the device having anexternal geometry complementary to the internal geometry of the channel.In typical embodiment of the method, repairing the access channelincludes implanting the bone repair device through the bone plate andinto the channel. And in some of these embodiments, the method includessecuring a proximal portion of the bone repair device to the bone plate.

In some embodiments of the method, repairing the access channel includesin-growing bone from the vertebral body into at least a portion of thesurface of the bone repair device. And in some embodiments, repairingthe access channel includes stimulating bone growth within the bonerepair device by providing an osteogenic agent within the repair device.

In some embodiments of the method, repairing the access channel includesplacing a portion of harvested native bone tissue within a bone repairdevice that comprises a porous cage. In these embodiments, the methodmay further include allowing or promoting intimate contact between thebone tissue within the bone repair device and bone tissue of thevertebral body. The method may further include perfusing at least somebone tissue or bone-associated biological fluid from the bone repairdevice into the vertebral body. Still further, the method may includehealing together the harvested native bone tissue within the bone repairdevice and bone tissue of the vertebral body.

In some embodiments of the system, the bone plate and the trajectorycontrol sleeve are an integrated or integrally-formed device. In thisembodiment, thus the system includes a bone cutting tool with a cuttingelement and an integrated device comprising a bone plate portion andtrajectory control sleeve portion. The bone plate portion is configuredto be secured to an anterior surface of the vertebral body and has anopening sized to receive the cutting element. The trajectory controlsleeve portion has a cylinder configured to receive the cutting elementof the bone cutting tool, and the integrated device is configured toguide the bone cutting tool to form the access channel with a prescribedtrajectory from the anterior entry to the prescribed posterior opening.

A method for performing a procedure through a vertebral body overlayinga site in need of a medical procedure with the integrated devicesummarized above includes attaching the integrated device on an anteriorsurface of the vertebral body, inserting a bone cutting tool through thetrajectory control sleeve portion of the device, forming an accesschannel through the vertebral body by removing bone with the bonecutting tool, the access channel prescribed as summarized above,disengaging the integrated device from the bone plate, and performingthe medical procedure through the access channel and the opening on theposterior surface of the vertebral body.

In some embodiments of the system and method, the bone plate orintegrally formed bone plate portion does not lie directly over theanterior entry location for the access channel. Rather, the bone plateor bone plate portion is attached to the anterior surface of thevertebral body adjacent to the entry location, and supports a trajectorycontrol sleeve or sleeve portion which may be located adjacent to theentry location.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a view of an implantable bone plate device viewed from ananterior perspective.

FIG. 2 is a view of an implantable bone plate device viewed from aposterior perspective.

FIGS. 3A and 3B provide views of a trajectory control sleeve attachment.FIG. 3A shows a trajectory control sleeve in a side view.

FIG. 3B provides a side cross-sectional view of the trajectory controlsleeve, showing how the angle of the sleeve relative to its base formsan asymmetrical opening in the base.

FIG. 3C shows the trajectory control sleeve from a proximally-directedperspective.

FIG. 4 is an anterior perspective of the trajectory control sleevemounted to an implantable bone plate.

FIG. 5 is a lateral view of the trajectory control sleeve mounted to animplantable bone plate.

FIG. 6 is a perspective view showing an implanted bone plate screwed avertebral body and with a trajectory control sleeve mounted thereon.

FIG. 7 is an anterior view showing an implanted bone plate screwed to avertebral body and a trajectory control sleeve mounted thereon.

FIG. 8 is a lateral view showing an implanted bone plate screwed to avertebral body and with a trajectory control sleeve mounted thereon.

FIGS. 9A-9B show various views of a trajectory pin and a drill depthgauge. FIG. 9A is a perspective view of a trajectory pin and a drilldepth gauge assembled together

FIG. 9B is a perspective view of an embodiment of the depth gaugesub-assembly.

FIG. 10 is a lateral view of the trajectory pin assembly shown in FIG.9A engaged in a trajectory control sleeve.

FIG. 11 is a cross sectional view showing a trajectory pin in fullengagement with vertebral bone and a trajectory control sleeve.

FIG. 12 is an anterior perspective view of a trajectory pin and depthgauge engaged within a trajectory control sleeve.

FIG. 13 is a cross section view showing a bone drill in positionrelative to a bone plate and trajectory control sleeve prior to cuttingbone tissue.

FIG. 14 is a perspective view of a bone plate after drilling has beencompleted and the trajectory control sleeve has been disengaged from theimplanted bone plate.

FIG. 15 is a perspective view of a spinal repair implant in thepre-insertion position relative to the implanted bone plate.

FIG. 16 is a perspective view of a spinal repair implant installed intoan access channel through an implanted bone plate.

FIG. 17 is an anterior perspective view of an alternate embodiment of animplantable bone plate.

FIGS. 18A and 18B are views of the trajectory control sleeve mounted onthe bone plate embodiment of FIG. 17. FIG. 18A shows the trajectorycontrol sleeve and bone plate from distally directed perspective.

FIG. 18B shows the trajectory control sleeve and bone plate from a sideview.

FIG. 19 shows an implantable bone plate in situ on a vertebral surface.

FIG. 20 shows a perspective view of an implantable bone plate andtrajectory control sleeve in situ on the vertebra surface.

FIG. 21 shows a drill cutter engaging vertebral bone tissue through thetrajectory control sleeve.

FIG. 22 shows an access channel through an implanted bone plate and intovertebral bone tissue.

FIGS. 23 and 24 show an intra-vertebral repair device engaging vertebralbone through the bone plate. FIG. 23 shows the repair device being heldby a surgeon immediately prior to inserting into the access channel.

FIG. 24 shows the surgeon's finger pressing the repair device throughthe bone plate and into the access channel.

FIGS. 25A and 25B show views of an intravertebral repair deviceembodiment with a proximal abutting surface orthogonal to the body ofthe device. FIG. 25A shows the device from a proximally-directedperspective.

FIG. 25B shows the device of FIG. 25A from a distally-directedperspective.

FIGS. 26A and 26B show views of an intravertebral repair deviceembodiment with a proximal abutting surface canted with respect to mainaxis of the body of the device. FIG. 26A shows the device from a sideview.

FIG. 26B shows the device of FIG. 26A from a proximally-directedperspective.

FIGS. 27A and 27B show views of an intravertebral repair deviceembodiment with a convex external profile, wider in its central portion,narrower at proximal and distal ends. FIG. 27A shows the device from aproximally-directed perspective.

FIG. 27B shows the device of FIG. 27A from a distally-directedperspective.

FIG. 28 shows the primary components of an exemplary system associatedwith the creation and repair of the intra-vertebral access channel.

FIG. 29 shows a typical access channel that may be produced with theinventive systems and methods.

FIG. 30 shows a cross sectional view of an access channel being formedin a vertebral body with a hollow cutting tool, a trephine, which formsan access channel with a removal bone plug.

FIG. 31 shows an exploded view of a bone repair device with a porousbody configured to hold bone tissue, and to allow compression of thetissue upon closing the porous body.

FIG. 32 shows a cut away cross sectional view of the bone repair deviceof FIG. 31 in assembled form.

FIG. 33 shows an external view of the assembled bone repair device ofFIG. 33 with bone tissue and associated fluid being extruded underpressure.

FIG. 34 shows an alternative embodiment of an assembled bone repairdevice with a porous body and with an internal pressure-amplifyingfeature.

FIG. 35 shows a bone repair device with a porous body containing bonetissue poised in a position from where it is about to be implanted in anaccess channel within a vertebral body.

FIG. 36 shows the bone repair device of FIG. 35 implanted in thevertebral body, and locked into a bone plate.

FIG. 37 shows a lateral cross sectional view of a bone repair devicewith a porous body containing bone tissue, in situ, within an accesschannel in a host vertebral body.

DETAILED DESCRIPTION

An inventive surgical system and associated method of use are providedfor transcorporeal spinal procedures that create and use an anteriorapproach to an area in need of surgical intervention, particularly areasat or near a site of neural decompression. Removal or movement of asource of compressing neural pathology is achieved via a surgical accesschannel created through a single vertebral body instead of through adisc space or through an uncovertebral joint (involving 1 or 2vertebrae). The access channel has a specifically prescribed trajectoryand geometry that places the channel aperture at the posterior aspect ofthe vertebra in at or immediately adjacent to the targeted compressingpathology, thus allowing the compressing neural pathology to beaccessed, and removed or manipulated. The access channel is formed withprecise control of its depth and perimeter, and with dimensions and asurface contouring adapted to receive surgical instruments and animplanted bone repair device.

The channel may be used to access and operate on the compressingpathology, more particularly to remove or to move a portion or the wholeof a herniated disc, an osteophyte, a thickened ligament, a tumor, ahematoma, a degenerative cyst, or any other compressing pathology. As apart of the procedure, the posterior longitudinal ligament posterior tothe transcorporeal access channel may be opened or removed through theaccess channel, thereby permitting the visualization or removal of anycompressing pathology otherwise obscured by the ligament.

The invention preserves native bone and disc tissue that is sacrificedby prior art procedures, and further preserves the natural motion of thevertebral joint. The procedure also preserves at least the anterior halfof the vertebral endplate of the vertebral body upon which the cuttingoccurs. Removal or the movement of the compressing pathology can proceedeven when a portion of the compressing pathology resides beyond thelimits of the transcorporeal access channel. Further, removal of thecompressing pathology may occur without inducing posterior or inwardcompression on the dura mater protective layer surrounding the spinalcord and exiting nerve roots, or exerting direct pressure on the spinalcord or exiting nerve roots. Also, the compressing pathology removal mayoccur without lacerating the dura mater protective layer surrounding thespinal cord and exiting nerve roots.

Embodiments of the system and method also pertain to therapeuticoccupation and repair of the vertebral body void created by making suchan access channel. This repair is achieved by inserting an implantablevertebral repair device that has a conformation complimentary to theinternal geometry of the access channel after the procedure is complete,and by securing the implant in the inserted position by means of avertebral bone plate. The external surface of the vertebral repairdevice is in substantial contact with the internal surface of the accesschannel after insertion is complete, thereby substantially restoringstructural and mechanical properties of the vertebrae. Such repairoccurs without directly or indirectly inducing compression of underlyingdura mater or neural structures. The repair further occurs without thesubsequent anterior migration of the vertebral repair device, whichcould cause injury to soft tissue structures located anterior to thespine.

In some embodiments, the implanted device has a bioabsorbablecomposition that allows replacement of the implant device by in-growthof native bone tissue, or which is incorporated into the native bonetissue. As a whole the system increases the objectivity ofconsiderations associated with spinal surgery, reduces patient risk, andcontributes to better and more predictable surgical outcomes.

Various aspects and features of the invention will now be described inthe context of specific examples and with the illustrations provided byFIGS. 1-37.

A number of tools and instruments are included in or used within thesystem and methods described herein. FIG. 28 shows some of these systemelements: an implantable vertebral plate 100, a cutting tool guide 200,a confirmation device or depth gauge 300, a collar 310 for theconfirmation device, a cutting tool 400, an implantable device 500, andan implant locking device 600.

An implantable vertebral plate 100 is adapted to attach to the anteriorsurface of a vertebra. A trajectory control sleeve 200 is adapted todetachably mount the implanted bone plate 100 to establish the entrypoint, trajectory, and depth of an access channel created through thevertebral body. A confirmation device 300 is adapted to temporarilyengage the cutter tool guide for the purposes of confirming placement ofthe trajectory control sleeve on the correct vertebra, for visualizingthe projected trajectory of the bone cutting device, and for measuringthe actual distance between the trajectory control sleeve and theanterior bone surface so as to accurately and predictably penetratethrough the vertebra without impinging on the dura-mater or other neuraltissue at the posterior aspect of the channel. The pin-shapedconfirmation device 300 is typically radio-reflective or radiopaque,thus allowing confirmation of all geometries on a surgical radiographtaken prior to the excision of any tissue.

A cutting tool 400 is generally adapted to remove bone material andcreate the vertebral access channel; the tool 400 has the precisecutting geometry necessary to produce the prescribed access channelgeometry within the vertebral bone. The access channel provides variousforms of advantage for aspects of procedures as described further below.

A surgical cutting instrument is used to open or partially remove theposterior longitudinal ligament which can obscure a view of thepathology of interest, but becomes observable by way of the accesschannel. A cutting tool used to remove osteophytes (bone spurs) at oradjacent to the base of the vertebral body can be approached by way ofthe access channel proximal to the neural elements to be decompressed.An instrument for grasping or moving herniated disc material or othercompressing pathology can be provided access to the site located at ornear the base of the access channel.

An implantable bone repair device 500 is adapted repair the vacantvertebral volume created by the formation of the access channel.

An implant locking device 600 is adapted to retain the implant in thedesired position. The locking device is adapted to positively engage theanterior surface of the repair implant and engagably lock it in placewith respect to the implanted bone plate device 100. Fasteners such aselements 600 and 900 (seen in later figures) are applied to retain abone plate or locking cap (see in other figures) in a desired position.

Each of these aforementioned system elements and their role in surgicalprocedures on the spine are described in further detail below.

FIGS. 1 and 2 show anterior and posterior views, respectively, of animplantable transcorporeal bone plate device 100 with a first oranterior facing surface 101 and a second or posterior facing surface102, the posterior facing surface being configured to be proximal or incontact with the anterior surface of a vertebral body afterimplantation. The device further has one or more holes 103 that form anaperture between surfaces 101 and 102 to accommodate and secureretention screws there to secure the device 100 to vertebral bone.

Embodiments of implantable bone repair described and depicted herein aremay include a multiple number of orifices, as for example, for insertingattachment elements, or for viewing, that have various sizes andtypically are circular or ovular in form. These are merely exemplaryforms and profiles of openings which may vary depending on particularsof the application of the device, such that size and profile may vary,and for example, by taking the form of any of circular, trapezoidal,multilateral, asymmetrical, or elongated openings.

The device also has a passage 104 for receiving and detachably-engaginga bone cutting guide device such as a drill or ream. The device 100further may have one or more engaging features 105 configured to receiveand engage a corresponding feature on the trajectory control sleeve in amanner that prevents relative motion of the trajectory control sleeveand its accidental disengagement from the implanted bone plate. Thedevice may have one or more protrusions 106 on the posterior surface(FIG. 2), the protrusions being adapted to impinge into or through thecortical bone so as to increase the stability of the implant on the boneand to allow for temporary placement of the device prior to insertion ofthe bone screws through the opening 103. Protrusions 106 further act tostabilize the bone implant and to transfer loads around the vertebralaccess channel after a surgical procedure is complete, thereby furtherreducing the risk of bone fractures or repair device expulsion.

FIGS. 3A-3C show a side view and perspective view, respectively, of anembodiment of a trajectory control sleeve 200 for a bone cutting tool, arotary cutting tool, for example, such as a drill, burr, reamer, ortrephine. FIG. 3A shows a trajectory control sleeve in a side view,while FIG. 3C shows the trajectory control sleeve from aproximally-directed perspective. The trajectory control sleeve 200 hasan internal cylinder 202 there through to allow passage of abone-cutting tool, such as a drill or trephine, and to establish andcontrol the angle a of penetration of the drill through a vertebralbody. As seen in FIG. 3B the angle a refers to the angular differencefrom a right angle approach with respect to the plane formed by animplantable bone plate 100 to which the trajectory control sleeve isengaged. More specifically, angle a can represent a compound angleaccording to a cranio-caudal axis and a medial lateral axis with respectto a reference plane tangential (such as would be represented by animplanted bone plate) to the access channel entry on the anteriorsurface of vertebral body. The angle a is prescribed by a physician bymaking use of radiographic images of the spine that focus on the targetvertebrae and the underlying pathology that are the subject of surgicalor diagnostic interest. Such procedures are typically performed prior tosurgery, and they may be repeated after the bone plate is attached tothe surgical site. FIG. 3C provides a cross sectional view of anexemplary control sleeve 200, which shows the tilt of the annular ring203 in accordance with angle α, and the consequent off-center opening atthe base of the trajectory sleeve, which generally aligns with the baseof the bone plate when the two components are engaged.

In some embodiments of the system and method, a transcorporal accesschannel is formed using a trephine type device such as those provided bySynthes, Inc (West Chester Pa.), which offers particular advantages. Thetrephine device produces a cylindrical channel through the vertebralbone while maintaining the core to be removed in an intact state. Thecore can be removed from the trephine after the tool itself has beenremoved from the vertebral body, and the bone tissue can be subsequentlyre-used as graft volume after the surgical procedure is completed.

Trajectory control sleeve 200 has a surface 201 adapted to be inintimate contact with and be co-planar to an anterior facing surface 101of a bone plate implant device 100 (after engaging the device, as inFIG. 4) so as to assure that the axial distance d is well establishedand controlled. The trajectory control sleeve 200 further has an annularabutting surface 203 surrounding the opening of the internal cylinder202, the surface being adapted to positively engage a correspondingfeature such as a flange or collar of the drill so as to prevent itsover-penetration into the vertebral body. This abutment may be internalor external to the guide device as shown in FIG. 4 and FIG. 3Arespectively. Trajectory control sleeve 200 also has an engaging andinterlocking feature 204 adapted to detachably-engage a correspondingfeature 105 (see FIG. 5) on the implantable bone plate 100. Thetrajectory control sleeve 200 is further generally adapted to protectsurrounding vascular and soft tissue from accidental injury or cuttingby providing a solid protective sheath around the sharp edges of thedrill while it is operating.

FIGS. 4 and 5 show a perspective view and side view, respectively, oftrajectory control sleeve 200 and an implantable bone plate 100 in theirmutually interlocked positions. FIG. 4 shows the internal cylinder 202for providing access, guiding and controlling the penetration of a drillinto vertebral bone. FIG. 4 further shows an alternate embodiment of thedevice that has an abutting surface 203, in which the abutting surfaceis internal to the trajectory control sleeve. FIG. 5 shows the planarengagement of the anterior surface of an implanted bone plate 101 withthe corresponding surface 201 of the trajectory control sleeve. Thisengagement establishes a reference plane 210 from which angle a anddistance d are controlled and referenced relative to the vertebral body.FIG. 5 further shows the engagement of the detachable locking features205 of the trajectory control sleeve and of the bone plate 105.

FIGS. 6-8 relate to the placement of a mutually-engaged bone plate 100and a trajectory control sleeve 200 to a vertebral body 230, inpreparation for creating an access channel through the vertebral body.FIG. 6 provides a surface perspective view of bone plate 100 in animplanted position on a vertebral body 230, the plate secured by a bonescrew 900, and further shows trajectory control sleeve 200 in itsengaged position on the bone plate 100. FIG. 7 shows an anterior view ofa bone plate 100 and trajectory control sleeve 200 mutually engaged and,the engaged assembly in it installed position on vertebral body 230. Abone screw 900 is inserted at or near the medial centerline 231 of thevertebral body 230, thus positioning the center point 220 of thetrajectory control sleeve cylinder at a prescribed distance 1 from thecenterline. As seen in FIG. 8, an angle β is the compliment to angle ashown in FIG. 5. After installation of the bone plate implant 100 on avertebral body 230, the reference plane 210 may be delineated relativeto the vertebral body 230 and as a baseline reference for the angle anddepth of drill penetration into the vertebral body.

FIGS. 9A and 9B show a pin or plug type confirmation device 300 used forconfirming vertebral position prior to excision of bone or other tissueand a collar 310 into which the confirmation device is inserted. Astandard procedure in spinal surgery is to insert a radiographicallyreflective screw or pin into the vertebral body and to take an x-ray ofthe cervical spine prior to beginning any procedure so as to assure thatthe procedure is being performed at the correct vertebral level. In theembodiment described the confirmation device 300 is slidably insertedwithin the internal diameter of the control sleeve 200 and progressedaxially therethrough until the proximal end of the device 300 is incontact with the anterior surface of the vertebral body. A radiographicimage is taken inter-operatively and reviewed prior to the excision ofany vertebral bone tissue. The examination includes an extrapolation ofthe trajectory through the vertebral body so as to confirm that theactual point of exit at the posterior surface of the vertebra is at thesurgically prescribed location. Further, the axial distance from theboth the anterior and/or posterior surfaces of the vertebra are measuredand used as references to control the depth of bone cutting necessary toproduce the access channel and to prevent over penetration into the duramater or neural tissue. In some instances the device 300 may be usedduring the bone cutting procedure as a checking device to determine theactual progression of the channel across the vertebra.

FIG. 9B shows a trajectory confirmation pin 300 and a collar 310 thatslidably-engages the external diameter of the pin by way of features 320that engage complementary features 321 on the internal diameter of thecollar. In this exemplary embodiment, the trajectory pin features 320are convexities that are complementary to concave collar feature 321.Collar 310 can slide axially along the length of the pin diameter 320and frictionally-engage the pin diameter in a manner that requires anaxial force to be applied to the collar to induce axial movement. Collar310 has a surface of engagement feature 330 that is adapted to makeintimate contact with the annular surface 203 of the trajectory controlsleeve when the pin is inserted into the trajectory control sleeve. Oncesurfaces 203 and 330 are engaged, insertion force F (FIG. 9A) applied bya surgeon causes pin 300 to travel axially through the internal diameterof collar 340, increasing the distance L2 between point 350 on the tipof the pin and the control surface 330 of the collar 310.

FIGS. 10-12 relate to the use of a trajectory confirmation pin 300, acollar 310, and trajectory control sleeve 200 in the context of a boneplate 100 in place, as implanted in a vertebral body 230. An embodimentof a pin device 300 is temporarily inserted into the internal cylinderof the trajectory control sleeve 200 and an x-ray is taken. The x-rayconfirms the location of the vertebral body 230 and ananterior-to-posterior extrapolation along the centerline of the devicethrough the image of vertebral body indicates the trajectory of thedrill or cutting tool and the projected point of exit at or near theposterior longitudinal ligament. Angular and distance measurements maybe made using the radiograph, and if adjustments are required, thesurgeon disengages the trajectory control sleeve and installs anotherdevice with the desired geometry.

FIG. 11 shows the confirmation pin 300 at its maximum depth ofpenetration through the transparently rendered trajectory control sleeve200 and bone plate implant 100. In this position, tip 350 of the pindevice is in intimate contact with the surface of the vertebral bone230. Because of the mechanical engagement of the collar 310 on theexternal surface, the collar remains in position relative thebone-contacting tip of the pin 350. Upon removal of the pin, distance L2(see FIG. 9A), as measured between the collar surface 330 and the pincontact tip 350, provides a reference dimension with which thepenetrating depth of the bone drill can be controlled by setting amechanical stop that engages the annular surface 203 of the trajectorycontrol sleeve. For ease of use, the surface of the confirmation pin 300may have linear graduations.

FIG. 13 shows a bone cutting tool 400, such as a drill, burr, or reamer,inserted through the trajectory control sleeve 200 and the bone plateimplant 100 with the tip of the cutting tool 420 at the initial point ofcontact on the vertebral body. Cutting tool 400 has a mechanical stop450. The distance D4 from the drill tip 420 to the lower surface 430 ofthe drill stop 450, is a prescribed dimension equivalent to the measureddistance L2 (see FIG. 9A) plus the desired depth of penetration into thevertebral body, such depth being established by the surgeon throughradiographic analysis.

FIG. 14 shows a surgical access channel 470 in a vertebral body 230, asviewed through the bone plate implant 100 after drilling has beencompleted and the trajectory control sleeve has been removed from theplate. After removal of the trajectory control sleeve, a neuraldecompression or other surgical procedure is performed through theaccess channel. On completion of the procedure, an intra-vertebral boneimplant 500 is inserted (FIGS. 15 and 16) into access channel 470 tofill an close it, restore mechanical strength and stability to the hostvertebral body 230, and to provide a medium within the vertebral bodysuitable for osteogenesis.

In some embodiments of the invention, the intra-vertebral access channel470 (FIG. 14) of an implantable bone plate has a diameter of about 5 mmto about 8 mm. This size creates a surgical field that is sufficientlyopen enough for typical procedures, and is sufficiently large enough tominimize the possibility that the access channel will not intersect thearea of neural compression. In some embodiments, the angle of entry aprovided by the access channel is about 10-30 degrees, with the centerof the point of entry being generally at mid-point on the cranio-caudallength of the vertebra. While these dimensions are typical, alternativeembodiments of bone plate implants may have varying widths andgeometries so as to accommodate wide anatomical variations. In variousalternative embodiments, trajectory control sleeve devices also mayinclude a wide range of angles and depths for the same reason.

With a combination of the angle of entry, the point of entry into thevertebral body, and the size of drill used to create the access channel470, some embodiments may result in a penetration of the posterior discspace in the posterior 20%-30% of the disc volume 480, leaving thevertebral end plate 490 and the native disc tissue 495 substantiallyintact. FIG. 29 illustrates a typical access channel 470 that may beformed using a 6 mm drill diameter, about a 10 degree angle of entry,with an entry point on the cranio-caudal centerline of the vertebralbody.

FIG. 15 shows an intra-vertebral implantable bone repair device 500positioned for implantation within the vertebra 230 through the boneplate implant 100. Various embodiments and features of a bone repairdevice are described in U.S. Provisional Patent Application No.60/990,587 of Lowry et al. (filed on Nov. 27, 2007, entitled “Methodsand systems for repairing an intervertebral disk using a transcorporalapproach”), which is incorporated herein in its entirety by thisreference. In the embodiment shown, implant 500 has an abutting surface520 adapted to engage with a corresponding surface of the bone plateimplant. This arrangement prevents excess penetration of the implantthrough the access channel and prevents the implant from compressivelyengaging neural elements. FIG. 16 shows the implantable device 500 inthe final installed position relative to the bone plate 100. The device500 has a locking mechanism 510, such as a conventional bayonet mount,for engaging the bone plate in order to prevent migration of the implantwithin or out of the access channel.

FIG. 17 shows an alternative embodiment 620 of an implantable bone plateas previously described and shown in FIGS. 1 and 2. In this presentembodiment, bone plate 620 has a larger lateral dimension to accommodateparticular anatomies that may be encountered, including those ofpatients, for example, with small stature, degenerative bone conditions,or osteophytes or other abnormalities that may require alternatefixations. To assure accurate location of the device relative to themedial centerline of the vertebra, implant device 620 may include aviewing port 650 or some other positioning indicator. FIGS. 18A and 18Bshow anterior perspective and side views, respectively, of theengagement of a trajectory control sleeve 200, as previously described,with the alternative bone implant device embodiment 620.

In another alternate embodiment, an implantable bone plate and bonecutting device may be formed as a unitary device and temporarily fixedto the vertebral body. In this embodiment an intra-vertebral accesschannel is created using the temporarily implanted device; subsequently,the device is removed, the surgical procedure performed, and the accesschannel repaired using the intra-vertebral implant as previouslydescribed. In this embodiment, a bone cutting device may have a leasttwo cutting diameters or widths, the first being that necessary toproduce the access channel, the second being a larger diameterconfigured to remove an annulus of bone on the anterior vertebralsurface so as to provide an abutting surface against which the implantwould rest in order to prevent over-penetration of the intra-vertebralrepair implant within the vertebra.

FIGS. 19-24 show exemplary devices being put to exemplary use toevaluate the practical viability, fit, and the functionality of methodsfor their use. FIG. 19 shows an implantable bone plate 100 in situ on avertebral surface 230. FIG. 20 shows a perspective view of theimplantable bone plate and trajectory control sleeve 200 in situ on thevertebral surface. FIGS. 21-24 include a view of surgeon's finger toshow scale and feasibility of manual manipulation of elements of theinventive system. FIG. 21 shows a bone cutting tool 400 engagingvertebral bone tissue through the trajectory control sleeve 200. FIG. 22shows an access channel 470 through the implanted bone plate and intovertebral bone tissue. FIG. 23 shows an intra-vertebral repair device500 being readied for engaging vertebral bone through the bone plate100.

FIGS. 25A-27B show embodiments of alternative external geometries of theintra-vertebral implantable devices 500 as may appropriate forparticular patients or procedures. FIGS. 25A and 25B show views of whatmay be considered a default embodiment of an intravertebral repairdevice with a proximal abutting surface orthogonal to the body of thedevice. FIG. 25A shows the device from a proximally-directedperspective, while FIG. 25B shows it from a distally-directedperspective. FIGS. 26A and 26B show and embodiment wherein abuttingsurface 520 is canted at an angle not orthogonal to the central axis ofthe device 500. FIGS. 27 a and 27 b show an intra-vertebral implantdevice 500 with a convex external profile where dimension D4 isnominally larger than the internal diameter of the access channel so asto compressively engage the cancellous bone tissue. Such a compressiveengagement can improve the interference fit of the device therein and tointer-diffuse cancellous bone tissue within the implant volume toimprove osteogenesis.

FIG. 28 shows an assemblage of some of these system elements, and wasdescribed at the outset of the detailed description; shown is animplantable vertebral plate 100, a cutting tool guide 200, aconfirmation device or depth gauge 300, a collar 310 for theconfirmation device, a cutting tool 400, an implantable device 500, andan implant locking device 600. FIG. 29 provides an exemplary embodimentof the invention that was discussed earlier in the context of theformation of an access channel, in conjunction with associateddescription of FIGS. 14-16.

Implantation of the patient's own bone tissue (an autologous graft) is agenerally advantageous approach to repairing bone, as autologousgrafting typically yields high success rates and a low rate of surgicalcomplications. Accordingly, some embodiments of the invention includeusing core bone tissue harvested from the forming of the access channel,and implanting the plug, intact, in the form of bone repair graft. Anadvantage to recovering and making use of bone derived from the channelincludes the absence of a need to harvest bone from a second site.Embodiments of the invention, however, do include harvesting bone fromsecondary sites on the patient, such as the iliac crest, as may beappropriate in the practice of the invention under some circumstances.In some embodiments, for example, it may be advantageous to supplementbone derived from the access channel with bone from other sites. Instill other embodiments, under various clinical circumstances, it may beappropriate to make use of bone from donor individuals. Bone from otherautologous sites or other donor individuals may be used as a repairdevice in the form of an appropriately formed plug, or bone may befragmented or morselized, and packaged as a solid plug, or bone may beincluded as a preparation provided in a porous cage, as describedfurther below.

Some embodiments of methods provided make use of a trephine type bonecutting system, as noted above. With a trephine bone cutting system, theexternal diameter of the bone tissue core is about equal to the internaldiameter of the trephine device, while the internal diameter of theaccess channel is about equal to the external diameter of the device.Thus, a trephine-derived bone plug from forming the access channelprovides an appropriately-sized piece to be inserted into the channelfor repair and healing, but does not necessarily make intimate contactwith the inside surface of the channel due to the width of the kerfcreated by the trephine.

Optimal healing and recovery from implantation of bone material into anaccess channel occurs when there is an intimate or compressiveengagement of the graft material with the vertebral bone tissue(substantially cancellous bone), as this intimate association providesfor rapid blood profusion and bone healing while providing mechanicalsupport during healing. Accordingly, an embodiment of the bone repairdevice provided herein includes a device with bone tissue inside aporous cage, as described in detail below.

The porosity of the cage is a particularly advantageous feature forallowing cell to cell contact through the boundary of the device. Tosome degree, it may also allow cell migration, however the mostadvantageous factor in promoting rapid healing is cell to cell contactthat initiates sites of tissue unification, which can then spread,stabilize a healing zone around the graft or bone repair device, andultimately lead to effective fusion and integration of the graft withinthe host vertebral body.

A porous cage, as provided by this invention, also has acompressibility, such that when the contents of the cage are subject toa compressive force, however transient and minimal, blood or plasma andbone cells that are present in the harvested cancellous bone are forcedoutward into the environment within and around the access channel site.Extrusion of biological fluid in this manner, advantageously packs bonetissue closer together within the cage, and bathes the periphery of thegraft and the host-graft intersectional zone with a medium that isoptimal for exchange of dissolved gas and nutrients that are critical inthe initial stages of healing. Some embodiments of the invention includebathing the bone tissue preparation in a supportive liquid medium beforeimplantation. Such bathing may occur prior to placing the bone tissuepreparation in the porous cage and/or after placing the preparation inthe cage. The liquid medium may be any appropriate cell culture medium,and may be further supplemented with biological agents, such asosteogenic agents or other growth factors.

Embodiments of the implantable porous cage bone repair device, asprovided herein, encapsulate the bone tissue contained therein, andprovide mechanical stability to the access channel during healing. Theseembodiments compensate for the volumetric loss associated with the bonecutting process of the trephine and promote contact between the bonevolume within the device and the surrounding vertebral bone tissue. Thedevice, as a whole, and like other bone repair embodiments provided,cooperates with the implanted bone plate so that the orientation andpenetration depth of the implant device within the access channel may becontrolled. These forms of control assure that the device does notover-penetrate through the channel, thereby compressing the dura materor neural elements within the vertebra, and assuring that the implanteddevice cannot migrate in an anterior direction out of the accesschannel.

Exemplary embodiments of the porous cage device and associated method ofuse will now be described in further detail, and in the context of FIGS.30-37.

FIG. 30 provides a cross-sectional view of a vertebral body 809 with abone plate 801 attached to the anterior bone surface 810. Mounted on thebone plate is a trajectory control sleeve 802 cooperating with the boneplate 801 to establish and control the trajectory of a bone cutting tool804 with a cutting surface 808 through the vertebral body to direct thetrajectory of the formed access channel to a prescribed point of exit atthe posterior surface of the vertebra 820, in the locale of a site ofmedical interest.

The depicted exemplary bone cutting tool 804 is a hollow bone cuttingtool, a trephine, with an external diameter 805 selected to becomplementary to the internal diameter of the trajectory control sleeve802, and to cooperate therewith so as to assure that the centerlines ofthe bone cutting tool and the trajectory control sleeve aresubstantially co-incident during the bone cutting process. The trephine804 progresses through the vertebral body 820 from an anterior toposterior direction until the cutting surface 808 penetrates thecortical bone at the posterior surface of the vertebra proximal to thespinal cord 850. Upon removal of the trephine from within the vertebralbody, a core of bone tissue within the interior of the trephine isextracted from the wound opening, thus creating or exposing an openaccess channel from the anterior surface of the vertebral body to theneural elements and the prescribed site of medical interest immediatelybehind the posterior wall of the same vertebral body.

FIG. 31 shows components of an exemplary bone repair device in alinearly exploded view from an external perspective. At the top, a cap950 is above a vertebral bone core 860; the bone core is positioned forplacement in a porous cage 900. FIG. 32 is a cross-sectional view of thefully assembled device 905. According to the inventive method, thevertebral bone core 860 is placed within an implantable intravertebralbone repair device 900 with a porous wall, and encapsulated by a cap orclosing element 950. In this exemplary embodiment the cap has a screwthread 951 disposed to engage a mating thread 901 on the body 900 of theimplantable device; the cap further has a compression element 952disposed to exert a compressive force F on the bone graft core 860 whenthe cap is being closed on the body 900 of the repair device, andconsequently inducing extrusion of native tissue within the device,through open pores 902 contained within the perimeter wall of theimplant device. As described above, the bone tissue placed within thebody of the repair device is not necessarily an integral bone plugintact from the trephine used to form the channel; the bone tissue maybe a fragmented or morselized preparation, it may include bone fromanother site on the patient, and it may include bone from another donor.

FIG. 33 provides an external perspective view of an assembled bonerepair device 905. This view captures a moment shortly after the cap 950has been closed, and by such closing has increased the pressure on thebone tissue contained within the device. By virtue of this elevatedpressure within the porous walled body 900, bone core graft tissue andassociated biological fluid are extruding through the porous perimeterwall. In some embodiments of the method, the cap 950 is closed on theporous body 900 of the repair device immediately prior to insertion ofthe assembled device 905 into the access channel within the hostvertebral body, and in some embodiments of the method, the cap is closedafter insertion of the porous body 900, thereby forming the completeassembly 905 in situ.

FIG. 34 shows a cross sectional view of an alternate embodiment of theporous body portion 900′ of an assembled repair device 905′ thatincludes an internal tissue expander feature 920 disposed to induceradial extrusion of the bone core tissue through the orifices.

FIGS. 35 and 36 show similar views of the porous cage device embodiment905 as were provided earlier by FIGS. 15 and 16 for solid bone repairdevice 500 embodiments. FIG. 37 shows a cross sectional view of theimplanted device 905 within an intravertebral access channel 470. Uponcompletion of the surgical procedure through the access channel, thebone repair implant assembly 905 (containing the harvested bone graftcore 860) is introduced into the transcorporal access channel throughthe aperture 830 in the implanted bone plate device 100. In oneexemplary embodiment, the bone repair assembly 905 has an abuttingsurface disposed to cooperate with a mating surface of engagement 871 onthe bone plate implant. The completed mating of the bone repair assembly905 with the bone plate 100 prevents the distal tip 890 of the implantassembly from penetrating into the spinal cord volume posterior to thevertebral body.

The implantable repair device assembly 905 further has an orientationand locking feature 951 disposed to engage a mating feature 950 on theimplantable bone plate 100 so as to control the radial orientation ofthe implant with respect to the bone plate and to lockably engage thebone repair implant device with the bone plate implant so as to preventmigration or expulsion of the bone repair implant assembly 905 out ofthe access channel. Such radial orientation of the implant relative tothe access channel may be particularly advantageous when the bottom ordistal end of the repair device body 900 is formed at an angle (notshown) to completely fill the access channel.

As a consequence of the implantation of the bone repair assembly 905within the access channel, the general mechanical integrity of thevertebral body has been restored, the internal void of the accesschannel has been filled in a manner such that native disc material 980cannot migrate into the channel, bone tissue (typically autologous) hasbeen re-implanted in a manner that establishes intimate contact betweenthe bone graft and the cancellous bone of the vertebra thereby promotingblood profusion and rapid bone healing.

What is claimed is:
 1. A surgical system to form an access channelthrough a vertebral body, the channel having an anterior surface entryand a posterior surface opening, the system comprising: a bone cuttingtool with a cutting element; and an integrated device comprising a boneplate portion and trajectory control sleeve portion, the bone plateportion configured to be secured to an anterior surface of the vertebralbody, the trajectory control sleeve portion having a cylinder configuredto receive at least a portion of the bone cutting tool, the integrateddevice configured to guide the bone cutting tool to form the accesschannel with a prescribed trajectory from the anterior entry to theprescribed posterior opening.
 2. The surgical system of claim 1 whereinthe bone plate portion includes openings to accommodate fixationelements to secure the bone plate portion to the anterior surface of thevertebral body.
 3. The surgical system of claim 1 wherein the trajectorycontrol sleeve portion is configured to direct the bone cutting tool onthe prescribed trajectory, the prescribed trajectory having an angleaccording to a cranio-caudal axis and a medial lateral axis with respectto a reference plane tangential to the access channel entry on theanterior surface of the vertebral body.
 4. The surgical system of claim3 wherein the angle is a compound angle.
 5. The surgical system of claim1 wherein the bone plate portion provides a reference surface andwherein the trajectory control sleeve portion may be configured with arange of angles formed with respect to the surface of the bone plateportion on two axes, a cranio-caudal axis and a medial lateral axis, therange of the angles varying between about 1 degree and about 30 degreesfrom a perpendicular angle.
 6. The surgical system of claim 5 whereinthe range of the angle varies between about 10 degrees and about 30degrees from the perpendicular angle.
 7. The surgical system of claim 1wherein the trajectory control sleeve portion includes a contact surfacefor engaging a corresponding surface on the bone cutting tool, thesurfaces configured so as to limit the penetration of the cutting toolinto the vertebral body to a prescribed depth.
 8. The surgical system ofclaim 1 wherein the posterior surface of the bone plate portion includesone or more penetrating elements configured to impinge into thevertebral bone tissue.
 9. The surgical system of claim 1 wherein thebone plate portion includes an anatomically-orienting feature toestablish the position of the bone plate portion relative to the medialcenterline of the vertebral body.
 10. The surgical system of claim 1wherein the bone-cutting tool is any of a drill, a ream, a core cutteror a trephine.
 11. The surgical system of claim 10 wherein the cuttingelement of the bone-cutting tool has a cutting diameter between about 5mm and about 7 mm.
 12. The surgical system of claim 1 further comprisingan implantable bone repair device having an external geometrycomplementary to the internal geometry of the access channel.
 13. Thesurgical system of claim 12 wherein the bone repair device is sized tobe insertable through an opening of the bone plate portion, the openingbeing sized to receive the bone cutting element.
 14. The surgical systemof claim 12 wherein the bone repair device includes a bio-compatiblematerial.
 15. The surgical system of claim 12 wherein the bone repairdevice includes a bio-absorbable material.
 16. The surgical system ofclaim 12 wherein the bone repair device includes an osteogenic agent.17. The surgical system of claim 12 wherein bone repair device includesreceiving features in or on its anterior surface configured toaccommodate the attachment of an insertion tool.
 18. The surgical systemof claim 12 wherein the bone repair device comprises a porous cage witha porosity sufficient to permit through movement of blood and bonecells.
 19. The surgical system of claim 18 wherein the composition ofthe porous cage comprises any of a polymer, a metal, metallic alloy, ora ceramic.
 20. The surgical system of claim 19 wherein the polymer ofthe composition may include polyetheretherketone (PEEK), PEEK-reinforcedcarbon fiber, or hydroxyapatite-reinforced PEEK.
 21. The surgical systemof claim 18 wherein the porous cage device includes a closeable openingthrough which bone material may be passed.
 22. The surgical system ofclaim 18 wherein the porous cage device includes a closeable capconfigured to increase pressure within the cage as the cap is closed.23. The surgical system of claim 18 wherein the porous cage deviceincludes a minimally compressive internal element adapted to enhancecompressive force applied to contents of the porous cage uponapplication of compressive force to the cage.
 24. The surgical system ofclaim 1 further comprising a trajectory and depth visualization device.25. The surgical system of claim 24 wherein the trajectory and depthvisualization device includes a radio-opaque feature to allowconfirmation of the location of the bone plate portion device on theappropriate vertebral body and to facilitate the extrapolation of theprojected trajectory of the bone cutting tool using a radiographicimage.
 26. The surgical system of claim 24 wherein the trajectory anddepth visualization device includes visual markings to indicate adistance from a point of contact with the vertebral body and cutterpenetration control feature on the bone cutter guide device.
 27. Asurgical system to form an access channel through a single vertebralbody overlaying a site in need of a medical procedure adjacent a spinalcord in advance of performing the procedure through the access channel,the channel having an anterior surface entry and a posterior surfaceopening, the system comprising: an integrated device comprising a boneplate portion and a trajectory control sleeve portion; and a bonecutting tool, wherein the bone plate portion of the integrated devicecomprises a curved surface configured to contact an anterior surface ofa single vertebral body and to be temporarily secured to the anteriorsurface of the vertebral body, wherein the trajectory control sleeveportion of the integrated device comprises a cylinder configured toreceive at least a portion of the bone cutting tool, wherein theintegrated device and the bone cutting tool are configured to cooperateto form a single access channel with a prescribed trajectory from ananterior entry to a prescribed posterior opening on a posterior surfaceof the vertebral body adjacent a spinal cord, the anterior entry of thesingle access channel having a center that is generally at a mid-pointon a cranio-caudal length of the vertebral body and generally offsetfrom a medio-lateral mid-point of the vertebral body, wherein the singleaccess channel to be formed has a circular cross-section along a single,straight axis from the anterior entry in a posterior, caudal and lateraldirection to the prescribed posterior opening, the prescribed posterioropening being located at or adjacent to the base of the posteriorsurface of the single vertebral body, the single access channel havingan angle in the cranio-caudal direction of between about 1 degree andabout 30 degrees from perpendicular to the anterior surface at theanterior entry, the single access channel having an angle in themedio-lateral direction of between about 1 degree and about 30 degreesfrom perpendicular to the anterior surface at the anterior entry, thesingle access channel having a diameter of between about 5 mm and about8 mm, wherein a portion of the cutting tool is configured to contact aportion of the integrated device to precisely limit the penetration ofthe cutting tool into the vertebral body to a prescribed depth.